The present invention relates to electrostatic printers and plotters employing liquid toner and, more particularly, to a unitary application/vacuuming head for a liquid toner electrostatic printing system comprising, a body having two planar faces angularly displaced from one another concentrically about a pivot point, one of the faces being a first tone face having openings therein communicating with a first network of toner passages in the body and the other of the faces being a vacuum face also having openings therein communicating with a second network of toner passages in the body; a pivot pin supporting the body for pivotal movement about the pivot point; and, pivot means for pivoting the body about the pivot pin between a first position with the first toner face in contact with a printing media being printed upon by the printing system and a second position with the vacuum face in contact with the printing media.
In the well-known xerographic photocopying process, copies of a document are made by optically viewing the document and creating an electrostatic copy of the document on a drum or belt. A powdered toner is then applied to the drum or belt, which toner adheres to the electrostatic charges in the pattern of the document. The pattern of toner is then transferred to a plain sheet of paper and fused to the paper with heat to create the desired copy of the document. Electrostatic printers and plotters employing liquid toner are less well known; but, are quite popular in the art, especially for larger documents and computer-degenerated outputs such as produced by Computer Aided Drafting (CAD) systems. Whether the device is a printer printing text or a plotter printing graphics the basic electrostatic operation is the same. Thus, for ease of terminology hereinafter, we will refer simply to a plotter with those skilled in the art recognizing that the present invention would work equally well in a printer.
A basic prior art electrostatic plotter employing liquid toner is shown in very simplified form in FIG. 1. The primary advantage of the plotter 10 of FIG. 1 over the above-described dry toner photocopying process is that there is no drum or belt. The electrostatic image is produced directly on the bottom surface of the copy paper 12. The paper 12 is typically a strip from a supply roll 14 moved back and forth over the elements to be described (as indicated by the arrow 16) to create the "plot" thereon by apparatus which is not shown in the drawing as being irrelevant to the present invention. An electrostatic charge is applied to the paper 12 by an electrostatic printing head 18 of a type well known to those skilled in the art. The paper 12 with the electrostatic charge on the bottom surface thereof then moves over a toner head 20 where liquid toner 22 from a sump 24 is circulated over the bottom surface of the paper 12 by a pump 26. The paper 12 with a film of the toner 22 clinging to the electrostatic charge on the bottom surface thereof then moves over a vacuum knife 28 where remaining excess liquid toner 22 is removed and returned to the sump 24 by a vacuum pump 30. If the printing process is in multiple colors, either multiple toner heads 20 and vacuum knifes 28 can be employed or the single toner head 20 and vacuum knife 28 can be purged with clear toner vehicle between colors. In either event, however, it can be appreciated that there is much forward and backward movement of the paper 12 and many parts involved in the process.
Wherefore, it is an object of the present invention to provide a unitary toner head and vacuum knife for use in an electrostatic plotter employing liquid toner so as to reduce the number of parts required in the plotter.
It is another object of the present invention to provide a unitary toner head and vacuum knife for use in an electrostatic plotter employing liquid toner so as to reduce the amount of forward and backward movement of the paper required in the plotter.
It is still another object of the present invention to provide a unitary toner head and vacuum knife for use in an electrostatic plotter employing liquid toner which can apply more than one color of toner in a single head without requiring purging between colors.
Other objects and benefits of the invention will become apparent from the description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.